1. Field of the Invention
The subject disclosure relates to systems and methods for rapid quantification and characterization of microbial colonization and biofilm formation on implants at the time of removal.
2. Background of the Related Art
Microbial infection and biofilm formation on orthopaedic trauma implants is one of the most serious problems in orthopaedic surgery. The formation of biofilms increases resistance to antibiotic treatment, and typically an orthopaedic device that becomes infected must be removed. In many cases, the heterogeneity of the tissue surrounding the complex surface of the implant may complicate the identification of microbial colonization or infection. Subsequent analysis to determine the bacterial colonization, adhesion, and species on the explant may take several days or weeks, negatively impacting the efficacy and efficiency of possible treatment plans. In many cases, current detection methods may yield false-negative findings, which further exacerbate the problem.
Based on projections from 2004, of an estimated two million fracture-fixation devices implanted annually in the U.S. the number of infected implants was greater than 100,000 cases, or 5% overall. The field of orthopaedic trauma encounters significantly higher rates of infection. With open fractures (fractures in which the bone has violated the skin and soft tissue) incidence of infection may exceed 30%. The overall infection rate of trauma patients is extremely high, with specific incidence depending on fracture type.
Furthermore, this infection rate dramatically increases in traumatic extremity injuries sustained during combat and in developing countries. Despite many strategies in infection treatment, including prophylactic antibiotic administration, surgical debridement and irrigation, and post-surgical antibiotic regimens, an orthopaedic device that becomes infected typically must be removed, or ‘explanted’.
These one- or two-step revision surgeries mean delayed healing time, increased medical costs, and less successful post-operative outcomes. One of the greatest ongoing challenges in the field of orthopaedic trauma remains decreasing the rates and consequent ill effects of bacterial infection.
One of the principal factors challenging effective infection treatment is the formation of bacterial biofilm, a coating of bacterial film that adheres to the infected tissue and/or orthopaedic implant. Biofilm formation proceeds as a four-step process: 1) initial attachment of bacterial cells; 2) cell aggregation and accumulation in multiple cell layers; 3) biofilm maturation and 4) detachment of cells from the biofilm into a planktonic (drifting) state to initiate a new cycle of biofilm formation elsewhere. Complexes of tightly attached bacterial communities follow, which display cell-to-cell signaling and exist within a strong extracellular polymer matrix.
Biofilms make bacteria more resistant to antibiotic treatment and enable them to cause recurrent infection. Biofilms are difficult to eradicate because most antibiotics are unable to penetrate their surface, weakening the primary line of attack. Additionally, biofilms make the enclosed bacteria resistant to many effects of the host's immune system. To combat biofilm-centered implant infections, new treatment strategies are being developed, including anti-infective or infective-resistant implant materials. Through modifying the biomaterial surface to give anti-adhesive properties, doping the material with antimicrobial substances, combining anti-adhesive and antimicrobial effects, or designing materials to oppose biofilm formation and support bone repair, biofilm formation can be markedly decreased.
Despite advances in infection treatment, one of the most comprehensive problems in fracture management and treatment is the need for rapid and accurate identification and quantification of microbial contamination or infection. There are several available clinical options for infection diagnosis, including the standard bacterial isolation and culture, and molecular processing techniques. In the standard isolation and culture method, swabs from multiple sites are taken from the affected area, cultured on plates in the laboratory, and isolated. However, a limited amount of bacteria swabbed or biofilm-adhered bacteria can decrease the probability of detection, yielding false-negative findings.
Because the bacterial swabs are grown and cultured in the laboratory, contamination from multiple sources during processing (e.g., surgeon, technician, other samples, laboratory environment) is possible. Importantly, analysis to determine the presence of bacterial colonization, adhesion, and species on the explant may take several days, contingent on the length of time the bacterial species requires to grow. This time lag between treatment and diagnosis, in addition to potentially faulty findings, negatively impacts the efficacy of current treatment plans.
Another diagnostic test less commonly employed is 16S rRNA molecular testing, which identifies pathogens based on analyzing and sequencing the bacterial 16S molecular marker. While this technique was found to have a high level of identification accuracy and specificity, these tests are not widely available, and identification of species requires bacterial sequencing and species-specific primers. Furthermore, molecular probes do not provide susceptibility testing, which predicts in vivo success or failure of a directed antibiotic therapy. Genomic probes—such as real-time PCR—are dependent on isolation, prone to contamination, and have a turnaround time of several hours to days. Additionally, these tests have been found to be more expensive than traditional bacterial culture and isolation techniques.